In the conventional method for producing a secondary battery such as a lithium-ion secondary battery and a Ni-MH secondary battery, an electrode body is made by laminating and winding a positive electrode sheet, a negative electrode sheet and separators interposed therebetween, and the electrode body is housed in a case. The electrode body is impregnated with an electrolytic solution in the case, and followed by predetermined steps such as a self-discharge and an aging.
As to the conventional production step of the secondary battery as mentioned above, JP 2004-132776 A discloses an inspection step performed to select a secondary battery with a micro short-circuit (defective product).
As shown in FIG. 9, an inspection step S100 for selecting the defective products from the plurality of secondary batteries is performed.
In the inspection step S100, first, a terminal voltage before the aging V0 and a terminal voltage after the aging V1 are measured (step S101), and a difference between them is calculated as a voltage difference ΔV in each of the secondary batteries (step S102).
Next, an average of the voltage difference ΔV between the terminal voltage V0 and the terminal voltage V1 that are calculated in each of the secondary batteries is calculated as an average value ΔVA (step S103). Moreover, a reference value ΔVB of the defective product is set (step S104).
Finally, a value obtained by subtracting the reference value ΔVB from the average value ΔVA is compared with the voltage difference ΔV in each of the secondary batteries (step S105), in the case where the voltage difference ΔV is lower than the value, the secondary battery as the test object is determined as the defective product (step S106), and otherwise, the secondary battery is determined as an acceptable product (step S107).
However, in JP 2004-132776 A, the micro short-circuit in the secondary battery is not determined by a physical explanation, that is, an explanation with an equivalent circuit, and the defective product is selected on the basis of the micro short-circuit considered as a decrement of voltage caused by the self-discharge, so that accuracy of the inspection is low, and an erroneous determination might be incurred.    [Patent Literature 1] JP 2004-132776 A